1. Field of the Invention
The present invention relates to a direct memory access technology and, more specifically, to a direct memory access technology when a plurality of requests compete with each other.
2. Description of the Related Art
Recently, microcomputers have remarkably increased in speed and function. Along with this, cost reduction has also been an important issue to attain low prices. For lower costs, it is necessary to reduce chips in size and packages in the number of terminals. Also in consideration of the response of a direct memory access (DMA), reducing the number of terminals, even if it is only one, is a challenge which leads directly to a reduction in cost.
FIG. 7 shows a configuration of a DMA device according to the prior art. A microcomputer 700 contains a CPU and a DMA controller (DMAC) to input and output a request signal REQ and an acknowledge signal ACK from and to a plurality of macros 701 to 703 respectively. Each of the macros 701 to 703 has an output terminal for the request signal REQ and an input terminal for the acknowledge signal ACK. The microcomputer 700 has input terminals for the request signals REQ and output terminals for the acknowledge signals ACK corresponding to the number of the macros 701 to 703.
Each of the macros 701 to 703 can make a DMA request to the microcomputer 700 by the request signal REQ. Upon reception of the request signal REQ, the microcomputer 700 determines acceptance or rejection thereof and outputs the acknowledge signal ACK to one of the macros 701 to 703 to perform DMA. In other words, the microcomputer 700 inputs and outputs the request signal REQ and the acknowledge signal ACK from and to each of the macros 701 to 703 individually.
However, when the macro is increased in number by 1, the terminal of the microcomputer 700 is increased in number by 2. Therefore, there is only one choice to be made, either abandoning DMA because of the limitation on the number of the terminals of the microcomputer 700 or increasing the terminals in number at a risk of an increase in cost of the microcomputer 700.